As a blue light-emitting phosphor which exhibits blue light emission when excited by an ultraviolet ray pr a vacuum ultraviolet ray, CaMgSi2O6:Eu2+ (hereinafter sometimes referred to as “CMS:Eu2+”) obtained by substituting europium for a part of calcium of diopside (CaMgSi2O6) is known. The CMS:Eu2+ blue light-emitting phosphor has a characteristic feature that the crystal structure is stable and emission efficiency decreases less with aging as compared with BaMgAl10O17:Eu2+ (hereinafter sometimes referred to as “BAM: Eu2+”) which is widely utilized as a blue light-emitting material of PDP (plasma display panel) or a rare gas lamp. However, as known, the emission intensity of the CMS:Eu2+ blue light-emitting phosphor is lower than that of the BAM:Eu2+ blue light-emitting phosphor. Accordingly, there has been a demand for development a CMS:Eu2+ blue light-emitting phosphor having high emission intensity.
A CMS:Eu2+ blue light-emitting phosphor is generally produced by mixing a calcium source powder, a europium source powder, a magnesium source powder and a silicon source powder in a predetermined ratio to produce a blue light-emitting phosphor having a diopside crystal structure, and firing the mixture of powders in a reducing atmosphere. For the purpose of increasing the emission intensity of the CMS:Eu2+ blue light-emitting phosphor, studies have been conventionally made to optimize the raw material powders for the production.
Regarding the method for producing a CMS:Eu2+ blue light-emitting phosphor having high emission intensity, Japanese Unexamined Patent Publication (Kokai) No. 2003-183644 discloses use of a silicon oxide powder having a BET specific surface area of 10 m2/g or more as the silicon source powder.
An object of the present invention is to provide a method in that a CMS:Eu2+ blue light-emitting phosphor having high emission intensity as: compared with conventional CMS:Eu2+ blue light-emitting phosphors can be produced in an industrially advantageous manner.